It is known that the charging voltage of a vehicle battery can be regulated by controlling the excitation current of the alternator as a function of the result of a comparison between the voltage actually output by the alternator and a given reference voltage.
The reference voltage may be constant, but it turns out to be desirable under certain conditions to vary said voltage as a function of temperature.
In a conventional type of circuit for obtaining a reference voltage that varies as a linear and decreasing function of temperature, the slope and the intercept of the straight line representing the value of the reference voltage as a function of temperature require at least three specific resistance values in the circuit to be determined by calculation or by experiment.
It will thus be understood that such a circuit is poorly adapted to being integrated in a silicon chip, particularly if it is desirable for the circuit to be capable of being parameterized for different characteristic curves of reference voltage as a function of temperature. If N represents the number of possible curves, it then becomes necessary to provide 3xN resistances and associated with fuses that can be actuated externally. The size and the cost of the integrated circuit are thus increased undesirably.
The present invention seeks mainly to mitigate this drawback of the prior art and to provide a circuit for generating a variable reference voltage in which one characteristic curve can be selected from a plurality thereof in a manner which is extremely simple and cheap.
Another object of the invention is to reduce the number of resistances and fuses that are required for obtaining a given number of possible slopes.